Air carrier flight crew reported improper troubleshooting to silence aural autopilot warning resulted in autopilot engagement below 50 ft. and with the yoke locking up and arresting the rate of descent during landing.
Synopsis
Air carrier flight crew reported improper troubleshooting to silence aural autopilot warning resulted in autopilot engagement below 50 ft. and with the yoke locking up and arresting the rate of descent during landing.
Narrative
I was the pilot flying on the ILS XX with the ceiling at 300 ft. I briefed my FO (First Officer) that I would wait a little longer to disconnect the autopilot until landing was assured; given the low ceiling. I disconnected the autopilot around 100 ft.; the audio warning confirmed the autopilot disconnect. I pressed the autopilot quick disconnect button a second time to silence the audio warning; but it remained. I clicked it several more times; without success. As we approached the threshold (50 ft.?); I asked my FO if she could try to silence it on her side. At the 20 ft. RA announcement; I pulled back on the yoke to arrest the rate of descent and that's when I first noticed resistance in the yoke. Immediately after; the yoke moved back on my input and I noticed a red autopilot annunciation on the FMA (Flight Mode Annunciator); which confused me somewhat as it shouldn't be there anymore; but I was busy concentrating on the runway and landing the aircraft. At 10 ft.; I felt the yoke lock up again and then very shortly after that we touched down smoothly and uneventfully. After touchdown; I noticed for the first time; my FO's hand hovering over the autopilot button on the guidance panel and that's when it became clear to me that we had landed with the autopilot on. I pressed the autopilot quick disconnect one last time; exited the runway and taxied to the gate uneventfully. During the debrief; I asked my FO what actions she had taken; after I asked her to if she could silence the autopilot audio on her side. She replied that she reached for the autopilot on the panel; as she thought that perhaps the autopilot hadn't disconnected properly. She also mentioned pressing the autopilot quick disconnect on her yoke. I then asked if she had pressed the autopilot button on the panel several times; which would explain the intermittent pressure on the yoke and the reappearance of the red autopilot on the FMA. She confirmed that she had. As part of the debrief; I went over those systems with her; and reiterated that only way to silence the autopilot audio is by pressing the autopilot quick disconnect button on the yoke. I also explained the following: Disengaging the autopilot by pressing the button on the panel is a non-normal disengagement and should not be used unless called for by a checklist. The normal autopilot disengagement is by pressing the autopilot quick disconnect button. I also stressed that at no point should the autopilot button on the panel be pressed below 50 ft.; since autopilot use is not authorized. Lastly; I did not consider a go-around while this was happening; for the following reasons: The first time I felt resistance at 20 ft.; it was not apparent that the autopilot had been re-engaged; as the pressure did release shortly afterwards and I thought that perhaps I [had] hit my FO's knees. The second time; at 10 ft.; the aircraft was stable; landing was assured and it did not; in my opinion warrant a go-around; given the weather conditions and FOB; which would have likely required us to go to our alternate of ZZZ1.Cause: During the debrief; it became clear to me that there was some confusion with regards to the audio autopilot warning and the autopilot controls. I think inexperience was a large factor. Weather conditions probably also contributed to higher stress levels; which might have led to the confusion.Suggestions: As the pilot flying; the autopilot audio was not a threat but more of a distraction/nuisance; and while it seemed like a reasonable request at the time to ask my FO if she could silence the autopilot audio on her side; in hindsight it probably introduced an unnecessary distraction.
Second reporter narrative
Captain flying; FO (First Officer) monitoring. On the ILS XX approach into ZZZ; Captain disconnects autopilot but could not silence the aural autopilot warning. Captain asks FO to silence the warning. The FO mistakenly presses the autopilot engage on the guidance panel 3 times before realizing this will not shut off the warning; resulting in the autopilot being turned on below 50 ft. AGL. FO presses autopilot disengage on FO yoke to silence the warning. Captain and FO debrief and correct FO's wrong assumption of autopilot button on guidance panel turning off aural warning. Cause: FO had wrong reaction to Captain's request.Suggestions: Captain and FO debriefed situation to mitigate similar mistakes in the future.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.